1. Field of the Invention
The present invention relates to an organometallic complex and an organic electroluminescence device, and more particularly, to an organometallic complex enabling red light emission and an organic electroluminescence device including an organic layer formed of the organometallic complex.
2. Description of the Related Art
Organic electroluminescent (EL) devices, which are active display devices, use the recombination of electrons and holes in a fluorescent or phosphorescent organic compound thin layer (hereinafter, referred to as ‘organic layer’) to emit light when current is applied thereto. Organic electroluminescent devices are lightweight, have wide viewing angles, produce high-quality images, and can be manufactured using simple processes. Organic electroluminescent devices also can produce moving images with high color purity while having low consumption power and low voltage. Accordingly, organic electroluminescent devices are suitable for portable electronic applications.
In general, an organic electroluminescent device includes an anode, a hole transport layer, an emission layer, an electron transport layer, and a cathode sequentially stacked on a substrate. The hole transport layer, the light emitting layer, and the electron transport layer are organic layers formed of organic compounds. The organic electroluminescent device may operate as follows. When a voltage is applied between the anode and the cathode, holes emitted by the anode move to the light-emitting layer via the hole transport layer. Electrons are emitted by the cathode and move to the light-emitting layer via the electron transport layer. In the light-emitting layer, the carriers recombine to produce excitons. The excitons radiatively decay, emitting light corresponding to a band gap of the material used to form the light-emitting layer.
Materials that can be used to form the light-emitting layer of the organic electroluminescent device are divided, according to the emission mechanism, into fluorescent materials using singlet excitons and phosphorescent materials using triplet-state excitons. The light-emitting layer is formed by such fluorescent materials or phosphorescent materials themselves or by doping such fluorescent materials or phosphorescent materials with appropriate host materials. When electrons are excited, singlet excitons and triplet excitons are generated in a host in the generation ratio of 1:3 (Baldo, et al., Phys. Rev. B, 1999, 60, 14422).
When fluorescent materials are used to form the light-emitting layer in the organic electroluminescent device, triplet excitons that are generated in the host cannot be used. However, when phosphorescent materials are used to form the light emitting layer, both singlet excitons and triplet excitons can be used, and thus, an internal quantum efficiency of 100% can be obtained (see Baldo et al., Nature, Vol. 395, 151-154, 1998). Accordingly, the use of phosphorescent materials brings higher light emitting efficiency than use of fluorescent materials.
When a heavy metal, such as Ir, Pt, Rh, or Pd is included in an organic molecule, spin-orbital coupling occurs due to a heavy atom effect, and thus, singlet states and triplet states become mixed, allowing forbidden transitions to occur and thus effectively emitting phosphorescent light even at room temperature.
As described above, transition metal compounds that include a transition metal such as Iridium (Ir) and platinum (Pt) have been developed to provide highly efficient phosphorescent materials that use a phosphorescence effect. However, development of red phosphorescent materials for full-color display devices is still required.